First, understand your DME is paid by insurance to send re-supply items. They will send as much as they can to ensure the bill is at the max the insurance payer will eat. Call the support folks at your insurance provider. I was on Humana until I started Medicare a couple years ago and they both sent about the same amount of stuff. I am not sure if there is some guideline they use so you can only contact your insurance. As far as how often to change stuff, I seldom change masks and it is usually because the headgear is shot as the mask part doesn't seem to wear. The cushion is another matter. I wash the cushion daily and over time it tends to make the cushion material a bit soft and the thing will leak a tad. After a few days of leaks, I change cushions. I do this perhaps once every 3 months or perhaps a bit longer. I get little filters for my ResMed Aircurve 10 and you are not supposed to wash them but I do. I almost never change hoses or water tanks; did change a tank about a month ago as it was leaking a tad. All in all, I get a bit more of this stuff than I actually use and have a good size pile of stuff. I think that gurus who suggest changing cushions on some sort of schedule are, well, (trying to find a nice way to say this), well not right. Change when needed. As far as liners, never heard of them by prescription. I used them with the Simplus mask and they are stupid expensive for bits of crudely cut out tee shirt material. I had to use them to keep air out of my eyes so used one of those several days till they got out of shape. I tried washing but they stayed out of shape and would likely have to be ironed to be suitable for reuse. I don't use them with my Amara View mask as I am leak free with this mask about half the nights and only have minimal leaking otherwise. Hope this helps...
Masks only need to be replaced when they don't work any more and, with a little TLC, this is usually a couple of years. Replacing stuff that is still working is a waste. Most of my patients never replace their hose unless it wears out ,as there is no need.
If your cushions aren't lasting 3 months that is very unusual. If you have oily skin, try cleaning your face before putting the mask on. It can increase longevity of you mask cushion and help prevent leaks.
Replacing mask cushions 1 - 2 times/month would be a massive waste, but your manufacturer would send you a Christmas card. Even the manufacturers only suggest once/year.
The instructions usually tell you to wash the mask every day. For most people this is unnecessary. The mask only needs to be washed often enough to keep it clean to a level that you are happy to use. It DOES NOT need to be sterile. For most people washing once a week is adequate. Washing every day will make your mask wear out faster. Also, you should only use luke-warm water as hot water will also decrease the life of the cushion. A useful alternative to washing can be baby wipes. Not those stupidly expensive CPAP wipes, which are a complete con, but simple, cheap, alcohol free (which is just about all of them these days) baby wipes. They are quite handy for cleaning during the week between washes. In the end it's all down to you. You need to balance the cleanliness you require from your mask with how often you want to replace it.
Of course, in your case you may have one of the flimsier mask designs. What kind of mask do you use?